One of the major challenges of motor control is to understand how the central nervous system controls the degrees of freedom of the body. This is particularly evident in cerebral palsy (CP), which is the most prevalent chronic childhood motor disability and is one of the most disabling and costly chronic disorders of children and adults. Deficits in postural control and sensorimotor integration are hallmarks of CP. Thirty-three percent of children with CP never achieve stable sitting balance in spite of current treatments. Although postural control of the trunk for independent sitting creates the foundation for all other motor tasks, surprisingly little is known about how infants use sensory input to guide their development of upright control (which typically occurs by 8 months of age). This lack of knowledge limits our ability to effectively assess and treat children with neuromotor deficits in trunk control. AIM 1 will identify sensory reliance and sensory reweighting in a longitudinal study of typically developing (TD) infants prior to, and during, development of stable sitting (1-8 months of age). AIM 2 will identify sensory reliance and sensory reweighting in a cross sectional study of children with moderate-to-severe CP (4-12 yrs of age). A novel trunk support device will enable testing of participants who lack (or are still developing) stable sitting. In experiments, kinematics of the head and trunk will be measured. Sensory reliance and reweighting will be identified from postural trunk responses to sensory conflict stimuli consisting of tilts of a visua surround and/or tilts of a surface which participants sit upon. Generally, participants with a high reliance on vestibular feedback will remain upright with respect to gravity during all tests; whereas a high reliance on cutaneous or visual feedback will produce trunk sway away from upright and toward the surface or visual surround tilt, respectively. To tease apart biomechanical, physical, and neurological contributions to trunk sway, sensorimotor integration modeling will be used to complement data interpretation. Knowledge obtained from this study will allow clinicians to develop new methods of assessment and intervention and may lead to creation of novel support devices for children with moderate-to-severe CP. The identification of sensorimotor integration during typical development will provide benchmarks for comparison with a variety of other neural or musculoskeletal deficits that affect trunk control, including CP.It is anticipated that, in addition to identification of sensory reliance, the rich data set collectedand quantitative model development will give insight into questions about sensorimotor noise, variability, system linearity, and internal models, generating pilot data and refining hypotheses for future R01 grants.